Full contact floating roof

ABSTRACT

A full contact floating roof for use in covering fluid bodies, such as storage tanks containing hydrocarbon fluids, allowing ease of construction, high integrity, and low maintenance cost.

TECHNICAL FIELD

[0001] The invention concerns a device for covering or sealing a liquidcontainment storage tank with a full contact floating roof.

BACKGROUND OF THE INVENTION

[0002] Liquid containment storage tanks are frequently used to storehydrocarbon liquids. When the stored liquid is volatile or presents arisk of pollution through evaporation, the storage tank is oftenequipped with a floating roof, which floats on top of the stored liquidand moves up and down with the liquid level. Floating roofs greatlyreduce liquid evaporation, preventing loss of the stored liquid andreducing pollution due to hydrocarbon evaporation into the atmosphere.

[0003] Such floating roofs are often provided with support legs whichare usually spaced about twenty feet apart and provide support to theroof when the roof is not floating on stored liquid, such as when thetank is emptied or taken out of service for maintenance. These roofs areusually floated by pontoons which are secured to the roof supportstructure. However, such pontoon-floated roofs leave a vapor space abovethe liquid surface in the tank. Thus, evaporation will occur in the tankuntil the vapor space is saturated, at which point equilibrium betweenthe vapor space and the liquid is reached.

[0004] However, there will be losses of the liquid stored in the tank,as vapor leaks through seams in the roof or around seals. Engineering offloating roofs attempts to eliminate such leakage losses, but theexistence of a relatively volatile vapor space immediately under theroof makes absolute elimination of such losses impossible.

[0005] Elimination of the vapor space is possible by using a fullcontact floating roof. Existing full contact roofs include aluminum andsteel roofs. Aluminum full contact roofs are usually comprised of panelsbolted to an aluminum framework. Such panels may comprise expandedaluminum honeycomb, or a foam core sandwiched between two layers ofaluminum sheet. Most full contact steel roofs are constructed from steelplate welded together and surrounded by steel pontoons. Other, “pantype” steel roofs are simple flat plate welded together with a verticalrim along the edge.

[0006] However, these types of full contact roofs have engineering andpracticality limitations. Current full contact roof designs are onlymarginally capable of sustaining the loads imposed on the structures.They are also easily upset and sunk if there is a large operationsanomaly in the underlying tank. Because these roofs have to beconstructed in the field, there are high labor and heavy-equipmentmachinery costs associated with assembling and moving materials aroundat the construction site. Further, steel roofs require periodicrepainting and are very susceptible to corrosion, creating highmaintenance costs and potentially limiting the useful life of the roof.

[0007] A further limitation of the aluminum honeycomb or foam coresandwiched-panel type roofs is the inability to test the individualhoneycomb cells for the presence of a foreign or combustible vapor. Suchvapor may be present if there is a leak in the outer sheeting cover.Moreover, the aluminum honeycomb or foam core sandwiched panels arenormally joined to the outer aluminum sheeting cover with glue oradhesive that frequently becomes brittle and inflexible after beingapplied. Cyclic operation of the floating roof, or certain externalloading conditions on the outer sheeting cover, such as walking on theroof, often cause theis glue or adhesive to crack, forming vapor orliquid paths between the individual compartments. Thus, the leak-tightintegrity of the individual compartments may be compromised.

[0008] Accordingly, it is an object of the invention to provide a fullcontact floating roof which is full contact, yet is made of relativelylightweight, durable, and stable materials which are easy to assemble.

[0009] It is a further object of the invention to provide a full contactfloating roof which is difficult to upset and sink.

[0010] It is another object of the invention to provide a full contactfloating roof which provides additional options for fire protection overexisting roofs.

BRIEF DISCLOSURE OF THE INVENTION

[0011] The invention comprises a full contact floating roof, constructedfrom a plurality of buoyant cells. In the preferred embodiment, thesebuoyant cells are formed by sections of extruded fiber reinforcedplastic (“FRP”). By creating a fluid and vapor-impermeable join betweenmultiple buoyant cells, groups of such cells are joined together side byside to form the roof. Although the shell, or body, of the buoyant cellscan be formed in any reasonable geometric shape which will still allowthe proper joins between cells, in the preferred embodiment the shellsare square-angle parallelepipeds, for example, box-like rectangularcells. Each cell must provide sufficient displacement so that the weightof the cell, plus any additional load the cell is expected to support,will float on top of the fluid which will be beneath the full contactfloating roof.

[0012] In the preferred embodiment, each cell is extruded with agripping slot on each side (as used herein, the cell's “bottom” isconsidered to be that side of the cell in contact with the containedfluid, the cell's “top” is that portion of the cell exposed to the openair or other atmosphere above the contained fluid, and the cell's“sides” are the sections of the cells which can be joined to othercells), into which can be inserted a formed, rigid or semi-rigid stripwhich, when inserted into the gripping slots of two of the cells, willmaintain the sides of those cells in close proximity to each other andwithout allowing substantial relative movement of the cells.Additionally, it is preferred that an adhesive sealant, glue, or epoxy,such as Pliogrip (Ashland Chemical) is applied to the side surfaces ofeach two cells being joined, so that the final join between the cellswill both be strong and provide a sufficient seal to prevent the escapeof contained fluid or vapor from the bottom of the cells.

[0013] Also in the preferred embodiment, the buoyant cells areapproximately two feet wide, and comprise interior risers which serveboth to support the top surface of the cell against applied loads and toform internal barriers, breaking the interior of the cell into a seriesof individual sub-cells. Because it is preferred that the buoyant cellsare extruded, the sub-cells created by the risers will run the fulllength of the cell, and will be sealed at either end with blocks ofmaterial such as Valox during assembly of the roof. Thus, each sub-cellcan independently provide a sealed airspace. These block seals areadditionally preferably glued in place with Pliogrip to insure acomplete seal.

[0014] This method of construction also allows the use of the same basicbuoyant cells to form any particular shape of roof. For example, acircular roof can be formed by cutting the necessary arc along the edgeof a series of joined buoyant cells, then sealing the exposed ends ofthe sub-cells. These cuts may be curved or may be miter cut in chords.The curved or chord cuts may be sealed in the same fashion as would aflat cut, thus allowing square, rectangular, circular, oval, elliptical,or other shapes of floating roofs to be formed using the same materialsand same construction methods.

[0015] Constructed in this manner, each sub-cell provides an independentflotation device. Further, the individual sub-cells can be flooded withgas, such as an inert gas, to improve fire protection when the floatingroof is used to contain volatile hydrocarbons. This process may beaccomplished economically by inserting a valve or a selectivelypluggable coupling through the top of each sub-cell. Moreover, aself-activating sealant or intermescent material such as Contega orFlameseal, for example, can be used to coat the interior of thesub-cells prior to sealing them, so that in the event of a fire abovethe roof, the individual sub-cells will close off and aid in preventingthe fire from reaching the contained fluid. Alternatively, insertscoated with such materials can be inserted in the sub-cells. Similarly,in the event of a puncture of the roof and subsequent fire, theintermescent material can act to expand and seal the hole, therebysuppressing the fire if it has reached the contained fluid.

[0016] Thus, this floating roof provides a variety of advantages overother such roofs. Because the extruded materials are relativelylightweight and can be shipped as individual cells, or pre-assembledinto sectional panels to be assembled on-site into a single roof, thecost and complexity of construction assembly on-site is greatly reduced.Further, the manner of construction, involving simple mechanical toolsand adhesives, greatly reduces the need for skilled labor on site, as isrequired to weld steel sections together or to assemble complex, bolted,aluminum frameworks. Moreover, the extruded materials provide furtheradvantages, because they are extremely corrosion resistant and thereforeprovide cost savings for long-term maintenance of the roof once it isinstalled.

[0017] The modular nature of the buoyant cells further allows eachsection to be tested for internal fluid or vapor leaks by providingsignal communication between a fluid or vapor detection device internalto the cell and a monitor outside the cell. Detectors can be placedwithin each sub-cell, and connected together by drilling or cuttingthrough the riser wall to allow a signal coupler, such as a wire orcable, to be passed between sub-cells. The integrity of the sub-cellscan be restored by gluing a seal in place around the signal couplerwhere it passes through the riser. Alternatively, test ports can beinserted in any sub-cell through the external skin of a buoyant cell,sealed in place, and connected to an external detection device to testthe sub-cell for fluid or vapor leaks.

[0018] Because holes from the top to the bottom of an extruded panel canbe sealed off from the remainder of the sub-cell or sub-cells thoughwhich the hole passes by means of seals and adhesives, it is alsorelatively easy to provide drains or manholes through a buoyant cell,allowing rainwater or other fluid to be drained away and allowing forinspection of the region under the floating roof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is an oblique top view of a full contact floating roofsubsection.

[0020]FIG. 2 is an end view of four extruded buoyant cells assembled asin FIG. 1.

[0021]FIG. 3 is an end view of an extruded, gripping slot of thepreferred embodiment.

[0022]FIG. 4 is an end view of one embodiment of joining two subsectionsof FIG. 1.

[0023]FIG. 5A is an end view of one embodiment of a buoyant cell.

[0024]FIG. 5B is an end view of one embodiment of a buoyant cell.

[0025]FIG. 5C is an end view of one embodiment of a buoyant cell.

[0026]FIG. 6A is an overhead view of the end seals for a rectangularbuoyant cell.

[0027]FIG. 6B is an overhead view of the end seals for a circular-roofbuoyant cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring to FIG. 1, a subsection 10 of a full contact floatingroof of the present invention is shown. The subsection 10 is comprisedof four square angle parallelepiped buoyant cells 12, which are joinedtogether by joins 14. Thus, the width 16 of the subsection 10 will beessentially four times the width of each buoyant cell 12, and the length18 will be essentially the length to which the buoyant cells have beencut. Because it may be convenient to pre-assemble subsections 10 awayfrom the final construction site, the length 18 of the buoyant cells 12can be determined by factors such as total weight of the subsection 10,shipping size limitations, or the dimensions of the overall roof to beconstructed.

[0029] In the preferred embodiment, the subsection 10 is provided with aframe 20 which around the perimeter of the subsection 10, allowing forincreased structural integrity for the subsection 10, and allowing foreasy attachment of lift points 22 to the subsection 10. If one or moreof the sides 24 of the subsection 10 will be in contact with the sidesof the fluid containment tank (not shown) in which the floating roofwill be installed, a primary 26 and secondary 28 seals are preferablyattached to those sides 24. To facilitate removal of excess loads, suchas rainwater, drains 30 may be inserted through one or more of thebuoyant cells 12, and sealed in place with adhesives to prevent leakagearound their perimeter.

[0030] Referring to FIG. 2, an end view of four buoyant cells 212,assembled as in FIG. 1, is shown. Each buoyant cell 212 comprises risers214 which extend the length of the buoyant cell 212, forming essentiallyindependent sub-cells 216. In the preferred embodiment, formed strips ofrigid or semi-rigid material 218 fit into extruded, gripping slots (seeFIG. 3) in the sides of the buoyant cells 212, positioning the buoyantcells 212 in a tightly held relationship to each other. Adhesive (notshown) is additionally used in each of the joins 219, to furtherstrengthen and seal the bonds between the buoyant cells 212. The sides222 of the subassembly 210 comprise a frame 220, which is preferablyformed of fiberglass or FRP with an extension 224 which fits into theextruded, gripping slots (see FIG. 3), and is preferably bonded furtherto the respective buoyant cell 212 with two-part urethane, preferablyPliogrip.

[0031] Referring to FIG. 3, an end view of the extruded, gripping slotin the side of a buoyant cell 312 of the preferred embodiment is shown.The slot 314 is formed by extrusion so that a formed rigid or semi-rigidstrip 316 can be securely slid into the slot 314, so that adjacentbuoyant cells may be securely joined together. As those of skill in theart will recognize, other means of attachment of the buoyant cells isfeasible, such as using bolts or screws, or using bridges secured to thetop or bottom surface of the buoyant cells. Accordingly, this depictionof the preferred embodiment of the extruded, gripping slot 314 is forillustrative purposes only, and is not intended to limit the scope ofthe invention.

[0032] Referring to FIG. 4, one method of joining two subsections suchas that of FIG. 1 is shown. The frames 410, 412 of the respectivesubsections 414, 416 are positioned so that a gasket, preferably aself-stick gasket 418 can be placed between them to form a seal, andtoggles 420 can be positioned at appropriate intervals down the lengthof the frames 410, 412 to securely tie subsections 414, 416 together.Thus, any number of subsections 414, 416 can be assembled side-to-sideor end to end, as necessary to form the needed area for the full contactfloating roof.

[0033] Referring to FIGS. 5A, 5B, and 5C, various configurations of theinterior of the buoyant cell 510 are shown. The sub-cells 512 may befilled with a gas through valves (or, alternatively, couplings) 513,such as an inert gas (not shown) to increase the fire-resistantqualities of the buoyant cell 510. Similarly, the interior walls 514 ofthe sub-cells 512 may be coated with an intermescent material 516 toprovide fire-proofing, or, in the case of a puncture of the buoyant cell510, fire-suppression. This coating can be easily accomplished byinserting a hose (not shown) with a spray attachment (not shown) downthe length of the sub-cell 512, then spraying the intermescent material516 while withdrawing the hose.

[0034] Further, fluid or gas probes 518 may be inserted in each sub-cell512 for leak detection purposes, and may be placed in signalcommunication with a detector (not shown) by providing a signal lead 520through a hole 522 (or slot, if at the end of the buoyant cell) in thewalls 514 of the sub-cells 512. Sealant or adhesive (not shown) may beplaced around the signal lead 520 where it penetrates the walls 514 toinsure the continued separation of the sub-cells 512. The signal lead520 can then be extended through the top 524 of the buoyant cell 510. Asthose of skill in the art will recognize, signal leads could be extendedfrom each sub-cell 512 rather than being joined in a single feed,without departing from the spirit of the invention. However, using asingle feed reduces the number of penetrating holes in the top 524.

[0035] Referring to FIGS. 6A and 6B, multiple configurations of theseals for the ends of the buoyant cells 610 are shown. Each sub-cell 612is sealed with a block 614 of material such as Valox, which ispermanently set in place with adhesive. If the shape of the roof isround or oval rather than square, or even an irregular shape, the endsof the buoyant cells 610 may be cut to shape as needed, as shown in theexample of a circular floating roof section of FIG. 6B. The sealingblocks 614 can then be cut to the shape of the end of each sub-cell 616,as needed. However, if the ends of adjacent sub-cells are sufficientlystraight, a single block 614 of material may be used to bridge and sealthe ends of more than one adjacent sub-cell (not shown).

[0036] Those of skill in the art will recognize that variations of theabove description may be made without departing from the scope andspirit of this invention, and this invention shall not be unduly limitedto these illustrative embodiments.

We claim:
 1. A full contact floating roof having a top, a bottom, and aperimeter, comprising a plurality of selectively interlinkable buoyantcells, comprising an interior and an exterior, and a linkage between atleast two of said cells, wherein said linkage and said cells areessentially impermeable to hydrocarbon fluids and vapors.
 2. The fullcontact floating roof of claim 1, wherein said buoyant cells comprisefiber reinforced plastic shells.
 3. The full contact floating roof ofclaim 1, wherein said buoyant cells comprise fiberglass shells.
 4. Thefull contact floating roof of claim 1, wherein said buoyant cells areformed by extrusion.
 5. The full contact floating roof of claim 1,wherein at least one of said buoyant cells comprises at least oneinterior riser.
 6. The full contact floating roof of claim 5, wherein atleast one interior riser essentially divides the interior of saidbuoyant cell into a first interior segment and a second interiorsegment.
 7. The full contact floating roof of claim 6, wherein saidfirst interior segment and said second interior segment are not ingaseous or liquid communication.
 8. The full contact floating roof ofclaim 1, wherein said interior contains a gas.
 9. The full contactfloating roof of claim 8, wherein said gas is inert.
 10. The fullcontact floating roof of claim 1, wherein said interior contains anintermescent material.
 11. The full contact floating roof of claim 1,wherein said interior is in signal communication with a vapor detector.12. The full contact floating roof of claim 1, wherein said interior isin signal communication with a fluid detector.
 13. The full contactfloating roof of claim 1, wherein said buoyant cells are essentiallysquare-angle parallelepipeds.
 14. The full contact floating roof ofclaim 1, wherein said linkage comprises a formed rigid strip, andwherein said buoyant cells comprise interlocks capable of securelyreceiving said formed rigid strip.
 15. The full contact floating roof ofclaim 1, wherein said linkage comprises an adhesive.
 16. The fullcontact floating roof of claim 1, wherein said linkage comprises afiberglass epoxy.
 17. The full contact floating roof of claim 1,additionally comprising a seal around the perimeter of said floatingroof.
 18. The full contact floating roof of claim 1, additionallycomprising lift points attached to said top of said floating roof. 19.The full contact floating roof of claim 1, additionally comprising adrain providing fluid communication from said top of said floating roofto said bottom of said floating roof.